Generally, in a manufacturing process of highly integrated semiconductor elements a resist film is first applied on an interconnection material such as a metal film which becomes an interconnection for electric conduction, and on an interlayer insulating film material which ensures insulation between interconnections. A desired resist pattern is formed by photolithography, dry etching is conducted using the resist film as a mask, then the remaining resist film is removed by plasma ashing and then wet treatment using a cleaner and residue remover composition to remove resist residue remaining on the interconnection material and the interlayer insulating material.
To fulfill the demand for faster processing speed from semiconductor, the conventional Al or Al alloy used as the interconnection material has been replaced with Cu or Cu alloy, typically using a known damascene process. A barrier film, which may be silicon nitride, and a Low-k film are successively formed on the substrate, and a resist mask is then formed. Next, the exposed Low-k film is dry etched to expose the barrier film, so that a via hole is formed. At this time, reactive products of the gas used for the dry etching and the Low-k film and the resist film accumulate in the via hole as resist residue. Then, the resist film is removed by plasma ashing, leaving a modified film on the surface of Low-k film according to the reaction of the resist to heat and plasma during ashing. Then the resist residue is removed by processing with a fluoride-based cleaning composition. To ensure the removal of the resist residue, a cleaning composition likely to evenly etch the insulating film has been used, and the via holes are enlarged. The common interlayer dielectrics, low-K dielectrics, CORAL, TEOS, SiOC, porous MSQ, SiON, and boron phosphosilicate glass (BPSG), which are commonly used in semiconductors for better conformity of step coverage, is usually removed with HF solutions. Now, however, conventional p-TEOS films or the like are being replaced with Low-k films having a lower dielectic constant than the p-TEOS film. Examples of the Low-k film currently regarded as promising include a film formed of inorganic material such as porous silica or the like, a film formed organic material such as polyimide, polyarylene or the like, and a film formed of a mixture of the above-mentioned inorganic and organic materials. Additionally, conventional i-line resists are being replaced with a chemically amplified excimer resist, such as KrF excimer resist, ArF excimer resist or the like, and a efficient cleaning composition for these new compositions is needed. Subsequently, a resist film patterned for trench formation is formed on the Low-k film, and, using the resist mask, the Low-k film is dry etched down to its intermediate position to form a trench. Resist residue that is the reactive product of the gas used for the dry etching and the Low-k film accumulates in the via hole and trench. The resist film is removed by plasma ashing, and resist residue is removed by processing with a conventional fluorine type compound-based cleaning composition. The conventional cleaning composition removes the resist residue and also etches the surface of the Low-k film, so that the internal diameter of via hole is further enlarged and the width of trench increases. Then, the barrier film, e.g., silicon nitride, is removed by dry etching to expose buried copper interconnections. Then, the surface of the copper interconnection is cleaned with a cleaning composition. In the conventional fluoride-based cleaning compositions, a copper corrosion inhibitor such as benzotriazole (BTA) has been added to prevent corrosion of the copper interconnection. With such a cleaning composition, however, there is a problem that the copper corrosion prevention interferes with attempts to improve the resist residue removing action. Finally, copper is filled in the via hole and trench by plating or the like.
Normally the fluoride-based cleaner and residue remover used as the last process step are called “RCA rinses”, and they beneficially remove monolayer amounts of metal, anions and/or organic contaminants and/or surface residues (e.g., particles). Using fluoride chemistries (usually HF) as a final RCA cleaning step will cause the silicon wafer surface to be in a hydrophobic state (the surface is covered with Si—H groups) which will repel water. During this step a certain proportion of the wafer surface is dissolved (removed). Unless the conditions are carefully monitored (time, temperature, solution composition) the substrates can be damaged, for example as the Low-k film is further etched to further narrow the interval between interconnections. This would cause degradation in characteristics, such as a decrease of driving speed of semiconductor element due to increased electric capacity between the interconnections, or a defect such as short-circuit between the interconnections. It is not uncommon for the HF to also attack the dielectric material. Such attack, which may include introduction of water, disruption of the structure, swelling, and the like, is not desirable. Accordingly, a need exists for a less damaging cleaning formulation.
The requirement for cleaning solutions that remove all types of residue generated as a result of plasma etching of various types of metals, such as aluminum, aluminum/silicon/copper, titanium, titanium nitride, titanium/tungsten, tungsten, silicon oxide, polysilicon crystal, and the like, while not corroding the underlying metal nor altering the dielectric presents a need for more effective chemistry in the processing area. The effect of poor cleaning results in low device yield, low device reliability, and low device performance.
It is desirable to develop an improved cleaning composition to remove the organic polymeric substance from a coated inorganic substrate without corroding, dissolving or dulling the metal circuitry or chemically altering the wafer substrate.
In addition, stripping compositions used for removing photoresist coatings and cleaning composition for removing post-etch residue have for the most part been highly flammable solvent mixtures exhibiting an undesirable degree of toxicity. Disposal is therefore costly.
There is also a need to remove particulate residues from the wafer surfaces during the BEOL process. The compositions are useful for post-CMP cleaning, particularly with substrates having tungsten.
There are five mechanisms for removing impurities (particles and/or ions) from the wafer surfaces:
1. Physical desorption by solvents, which involves replacing a small number of strongly absorbed particles with a large volume of weakly adsorbed solvent (changing the interaction of the surface charges);
2. Change the surface charge with either acids or bases, i.e., the Si—OH group can be made positive or protonated with acid or made negative with bases by removing the proton;
3. Ion complexion by removing adsorbed metal ions by adding acid (i.e., ion exchange);
4. Oxidation or decomposition of impurities, which involves oxidation of metals, organic materials or the surface of slurry particles, will change the chemical forces between the impurities and substrate surface. The chemical reaction can either be through redox chemistry or free radicals; and
5. Etching the oxide surface, which releases the impurity while dissolving a certain thickness of the substrate surface.
Currently available fluoride-based chemistries can help in items #2 and 5, but the cleaning conditions must be carefully controlled. Accordingly, there exists a need to develop improved cleaning compositions to efficiently clean a variety of deposits from a wide variety of substrates. Particularly in the field of integrated circuit fabrication, it should be recognized that the demands for improved cleaning performance with avoidance of attack on the substrates being cleaned are constantly increasing. This means that compositions that were suitable for cleaning less sophisticated integrated circuit substrates may not be able to produce satisfactory results with substrates containing more advanced integrated circuits in the process of fabrication. The cleaning compositions should also be economical, environmental friendly and easy to use.
The present invention teaches such a new and improved cleaning composition and a process for its use. This composition is aqueous, meaning it contains some water. This formulation dissolves both organic and inorganic substances, and, when used in the process, is able to clean a variety of substrates without damage.
It is a general object of the invention to provide a semiconductor substrate cleaning composition that is effective at low temperatures, e.g., less than 40° C., preferably less than 30° C., for example, ambient temperatures. It is a further object of the invention to provide a post etch residue cleaning composition that inhibits re-deposition of metal ions. It is a further object of the invention to provide such a cleaning solution having low etch rates of metal or metal-containing semiconductor layers, particularly metallic or reactively etched layers of copper or low-k dielectrics. It is a further object of the invention to provide such a cleaning solution and a process which removes post etch residues from metal structures. It is a further object of the invention to provide such a cleaning solution and a process which removes post etch residues from vias. It is a further object of the invention to provide such a cleaning solution and a process which removes post etch residues from low-k dielectrics, e.g., CVD-SiON films. It is further an object of the invention to provide a cleaning solution, which has reduced tendency to etch or to alter the low-K dielectrics. These and related objects are attained through the use of the composition and process disclosed herein.